1. Technical Field
The present invention relates to a method of manufacturing a composite carbon sheet by coating an expanded graphite sheet with a mixed dispersion solution, and, more particularly, to a method of manufacturing a composite carbon sheet by applying a mixed dispersion solution including carbon nanowires, a dispersant, a binder and the like onto one side or both sides of an expanded graphite sheet.
2. Description of the Related Art
A conventional method of manufacturing an expanded graphite sheet includes the steps of: charging expanded graphite powder in a mold; pressing the expanded graphite powder at a predetermined pressure to form a primary product; rolling the primary product to a target thickness to form a secondary product; and cutting and bending the secondary product.
The above method of manufacturing an expanded graphite sheet is processed as follows.
Expanded graphite powder is charged in a mold, and is then pressed at a predetermined pressure to form an expanded graphite sheet.
However, this method is problematic in that, since the manufactured expanded graphite sheet has low strength, it is plastically deformed when it is pressed at a predetermined pressure or higher, and in that the thermal conductivity of the expanded graphite sheet in a horizontal direction is high (100˜400 W/mk), but the thermal conductivity thereof in a vertical direction is low (3˜5 W/mk) because the expanded graphite sheet is porous. Further, a conventional expanded graphite sheet is problematic in that it is expensive because it is entirely imported.
Meanwhile, another method of manufacturing an expanded graphite sheet comprises the steps of: enlarging the gap between graphite particles using sulfuric acid; removing the clay remaining in the gap using hydrofluoric acid; expanding the graphite particles using high heat of 600˜1800° C. to form expanded graphite flakes; vibrating the expanded graphite flakes to form an expanded graphite flake layer; and continuously rolling the expanded graphite flake layer to produce an expanded graphite sheet. However, the expanded graphite sheet easily exfoliates. Therefore, a protective tape made of PE or PET is attached to one side of the expanded graphite sheet, and a double-sided tape made of PE or PET is attached to the other side thereof.
However, this method is also problematic in that pores are partially formed on the inside of the manufactured expanded graphite sheet and on the surface thereof, because the gap between the expanded graphite flakes cannot be completely removed, and in that the manufactured expanded graphite sheet easily exfoliates because of the inherent characteristic of graphite. Therefore, there is a problem in that the thermal conductivity of the expanded graphite sheet in a horizontal direction is high (100˜400 W/mk), but the thermal conductivity thereof in a vertical direction is low (3˜5 W/mk) because the density of the expanded graphite sheet is low.
Meanwhile, Korea Patent Registration No. 0628031 discloses a composite carbon sheet having high thermal conductivity, comprising: a carbon layer that is formed by pressing a mixture of expanded graphite powder and carbon nanotube (CNT) powder at high temperature; and a synthetic resin layer that is formed on at least one side of the carbon layer, which reinforces the carbon layer and which electrically insulates the carbon layer.
However, the composite carbon sheet is problematic in that the thermal conductivity thereof cannot be maximized because carbon nanotube particles cannot be charged between expanded graphite particles.
Further, the composite carbon sheet is problematic in that the thermal conductivity thereof cannot be maximized because an expanded graphite layer, a carbon nanotube layer, an adhesive layer, a heat-resistant film layer and a release paper are sequentially formed and thus the contact resistance between the layers increases.